Testing state composition

state.test.js

// reset state module for each test
let state;
beforeEach(() => {
  jest.resetModules();
  state = require('./state');
})

test('visibleTodos$ contains todos filtered thru visibilityFilter', () => {
  const { todoLib, visibleTodos$ } = state;
  todoLib.addTodo("First");
  todoLib.addTodo("Second");

  visLib.setVisibility("active");
  expect(visibleTodos$.value).toHaveLength(2);

  visLib.setVisibility("completed");
  expect(visibleTodos$.value).toHaveLength(0);

});